Thanks, but as a proof of concept (wf?) I checked my playthrough karma and had +800, then went on the rampage within Rivet City.

I picked every 'red' lock, pried into every terminal, and stole everything not tied down when nobody was looking. I gave chems to Pauli, even ratted on Mei Mei to Sister, then killed Sister (to no karma effect) in the market when it was closed (and nobody seemed to care; guess they didn't like Sister...). But the cherry-on-top was kicking Lopez off the observation deck.

I became the scourge of Rivet City with -680 karma in a matter of less than 1 hour playtime. I suggest to OP that a mod, or even a super-secret mystical karma quest bobble head, are not required to get this job done. You just have to effectively channel your inner @sshole...